1. Field of the Invention
The subject invention relates to plasma chambers and, more specifically, to the construction of a SiC (silicon-carbide) gas distribution plate, typically named “showerhead” and electrode (RF active or grounded) in plasma etch chamber.
2. Related Art
Plasma chambers are used, for example, in semiconductor fabrication process for etching and deposition of various layers of a specimen, such as a semiconductor wafer. To generate plasma in such chambers, the interior of the chamber is evacuated, precursor gases are injected into the chamber, and RF energy is coupled into the interior of the chamber to generate the plasma. In general there are two types of etch plasma chambers: inductive-coupled and capacitive-coupled plasma chambers. In inductive-coupled plasma chamber the RF energy is coupled into the plasma largely inductively for plasma generation; while in capacitive-coupled plasma chamber the RF is coupled into the plasma largely via capacitive discharge through RF active surface such as a shower head or a cathode.
FIG. 1a depicts an example of an inductive-coupled plasma chamber which may be used, e.g., for etching a wafer in semiconductor fabrication. In this example the coils 105 are provided over the roof section 115 of the chamber, although in other variations the coils may be provided about the sidewall 120. To couple RF energy from the RF source 110, the roof section 115 is typically made of a dielectric material having high electrical resistivity, which allows effective RF energy penetration and coupling. The RF source 110′ is connected to cathode to provide the bias power. Gas injection is then provided by means of injectors 125 provided from the side of the chamber, or the center portion of the insulator roof 125′, or below from bottom of the chamber. FIG. 1b illustrates a typical capacitive-coupled plasma chamber. RF energy from the RF source is applied to either top electrode assembly 145 (includes top electrode 140 and temp control unit 141) as shown by RF source 130, or to cathode 135 as shown by RF source 130′, or both. When RF is applied to the top electrode assembly 145, the cathode 135 serves as the ground for 130. Conversely, when the RF source 130′ is applied to the cathode 135, the top electrode assembly 145 serves as ground for 130′. Usually 130 and 130′ may have different RF frequency; in some cases, 130′ may have 2 or more frequencies. In both cases, the chamber walls also serve as round. The gas injection is generally done via the roof section 145, where a gas distribution plate (shower head) 140 and temperature control unit 141 are generally used to supply process gases. Currently, the majority of showerheads are made of single or poly-crystalline doped Silicon, and thus a consumable part subjected to plasma erosion.
It has previously been proposed to use Silicon Carbide, SiC, as an excellent alternative material for making the roof or the wall section of an inductively coupled plasma chamber for its electrical properties, purity and mechanical strength. It has been suggested that the part that is interposed between the coil and the interior of the chamber, i.e., the roof when the coil is placed over the roof, and the wall, when the coil is provided on the side around the wall, should be made of sintered SiC, coated with CVD SiC. More specifically, it has been suggested that the sintered SiC be made to have a high electrical resistivity so as to allow RF coupling from the coil to generate plasma. It has been further suggested that the CVD SiC coating be made of low electrical resistivity, i.e., conductive, so that it may be grounded to remove bias currents caused by the RF coupling from the cathode. Further relevant information can be found in, for example, U.S. Pat. No. 5,904,778, and other patents cited therein, all of which are incorporated herein by reference in their entirety.
As it happen, much of the industry has adopted the capacitive-coupled plasma chamber for certain applications, such as dielectric, polysilicon and metal etch applications of semiconductor wafers. However, since the sintered/CVD SiC previously proposed has properties more befitting the inductively-coupled plasma chambers, it has not been widely used for a capacitive-coupled chambers, except for the cathode edge cover rings 147 (FIG. 1b). In fact, the properties of the prior art sintered/CVD SiC structure are opposite to those required for a roof section of a capacitive-coupled plasma chamber. For example, the prior art sintered SiC base material is of high electrical resistivity, which would significantly reduce or prevent capacitive coupling of RF energy effectively and efficiently into plasma. Moreover, there has never been a suggestion that a showerhead can be commercially manufactured and available using the integrated sintered SiC/CVD SiC process.